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Astron. Astrophys. 336, 769-775 (1998)

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1. Introduction

Most of the work on oscillations of the interplanetary medium deals with the interaction between the solar wind and the interplanetary magnetic field (see e.g. Nakariakov et al. 1996 and Orlando et al. 1997 for recent theoretical work as well as Tu & Marsch 1995 for a comprehensive review). Magnetic field changes induced by the interaction of comet Giacobini-Zinner with the solar wind were extensively studied with the International Cometary Explorer (e.g. Smith et al. 1986, Scarf et al. 1986, Moses et al. 1992).

Analysing in situ measurements from Ulysses and
Voyager 2, Thomson et al. (1995) found the particle flux of the solar wind oscillating in the frequency range of the solar g and p modes, but the solar origin of the g mode signal was subject to some doubts (Kumar et al. 1996). While the determination of g modes requires observations of a very long duration 1, p-mode periods are short enough to allow the use of the classical solar-wind probe: a comet (see Flammer et al. 1997 for a summary of the interaction processes of Hale-Bopp with the solar wind).

With changes on the time scale of a few minutes, p-mode like oscillations are clearly separated from the time scale of typical cometarian effects like rotation, evaporation, etc. (see Rodriguez et al. 1997 for Hale-Bopp's variability). The report of such oscillations, already given by Isserstedt & Schlosser (1975) on the basis of observations of comet 1973f (Kohoutek) encouraged us to verify p-mode like oscillations in the solar wind by observing comet Hale-Bopp (C/1995 O1). While Isserstedt & Schlosser (1975) had more (11) nights under acceptable weather conditions, our Hale-Bopp data sets - taking advantage of a CCD camera - are improved with respect to their one-channel photometer observations in two ways: a posteriori corrections for tracking errors of the telescope are possible, and the two-dimensional field of view gives the opportunity to track the spatial evolution of conspicuous events. Apart from the enhanced accuracy, we do not only present data from the comet's coma but also analyse both ion and dust tail.

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© European Southern Observatory (ESO) 1998

Online publication: July 20, 1998